Tank structure for liquid treatment



l.. w. BIEKER Erm. 2,419,004

TANK STRUCTURE FOR LIQUID TREATMENT April 1s, 1947.

2 Sheets-Sheet 1 med June 9, 1944 INVENTORE. lazl/refzceWL'e/cer, BY Edd/afd W Efe/0,

'P 15,1947- L. w. BIEKER Erm. 2,419,004,

TANK STRUCTURE FOR .LIQUID TREATMENT 2 sheets-shan 2 Filed June 9, 1944 INVENTRQ. Law/'ence W Ekef BY ida/@rd w wel@ A fdJ 1% lem? Patented Apr. l5, 1947 -UNTED STATE s PATENT carica- TANK STRUCTURE FOR LQUID TREATMENT Lawrence W. Bicker, Munster, Ind., and Edward ,l W; Welp, Chicago, Ill., assignors to Graver Tank & Mfg. Co., Inc., a corporation of Delaware a claims. (c1. zio-' is) This invention relates to liquid treatment ap' A support the tank, its outer wan Il and its conparatus, and particularly to a sludge blanket device for accelerated precipitation.

It is an important object of our invention to provide such a device which is efiicient in operation and at the same time economical to build.

A specific object is to economize b`y using certain parts for a variety of structural and func-A tional purposes at the same time. y

Another specific object is to provide improved and simplified control means in such a device.

Still another object is to provide such a device with a maximum use of pre-fabricated parts.

In the drawing, Fig. 'l is an elevation, partly in' section, of an embodiment of our invention. Fig. 2 is a partial, sectional view taken along lines 2-2 in Fig. l and showingdetails thereof. Fig. 2`A shows a slight modiiication of the details of Fig. 2, in a similar view. Fig. 2-B is a section through Fig. 2A along lines B-B. Figure 2-C is a section through Figure 2 along lines C-C. Fig. 3 is an enlarged and slightly modified detail of further parts appearing in Fig. 1. Fig. 4 is a sectional detail from Fig, 3. -The section is taken along lines 4-4 in Fig. 3. Fig. 5 is an enlarged detail of other parts in a modi fied embodiment.

Our tank IU-has an outer, cylindrical wall II of steel. and a steelV bottom I2 in the form of aninverted cone with .slight inward inclination. The top of the tank is open. Hollow, semi-cylindrical members I3 are provided on the outside of the wall I I, preferably at uniform distances from one another, and extending vertically from adjacent the bottom I2 to above the bottom and be.

semi-cylindrical members extend' along and areA integrally secured to said wall by continuous iillets I4 of weld material so that the outside of the tents above the ground lIl-A.

Each half-pipe I3 rests on an individual column, concrete post or foundation member I5. Thus it canvbe said that the tank I0 has hollow pilasters I3, secured to the outside of its vertical side wall II and resting on columns I5, whereby the tank is supported. Welded elbow and support fittings lI6 are interposed between the bottom end of each half-pipe I3 and the top of the respective post I5, and shims Il may be inserted to level the tank I0. One part of each elbow ntting is welded to the respective half-pipe, while the other parts are directed toward the center of the tank. Each elbow I6 may consist of plate sections I6-A and IG-B suitably cut and formed and welded together along the line IG-C. The section I6A may have its top or outlet portv welded to the bottom of a half-pipe I3 along the line lI6`D, while the section IS-B may have its free end or inlet port IS-E directed toward the center of the tank.

In the lower, central part of the tank, a distributing sump I8 is formed by a cylindrical, apertured steel walll I9,` depending from the bottom I2 and surrounding this sump; the bottom I2 having a circular opening corresponding with of the tank. Radial, vertical vanes 24 are welded tank cooperates with said members to form conduits. 'Ihey are conveniently made by amecutting commercial steel pipes longitudinally, andare therefore referred to as half-pipes. At least three such half-pipesl I3 must be provided, so that they can Aserve as structural supports. These half-pipes together with the tank form conduits, as mentioned, and four or six or more such conduits are desirable, in some instances. They are uniformly distributed around the tank. Our tank, in its preferred form as shown can be designated as an elevated liquid treatment tank, having members I3 which simultaneously serve as conduit members for the liquid'treatment, and

to the outside of the nipple 22 and'to the inside of the guide 23, above the bottom plate- 20, and below the top of the guide 23.

The apertures 25 in the cylindrical wall are semi-circular, with the diameters parallel to the plane of bottom I2 andadjacent thereto. These openings correspond to the half-pipes I3 in num:

Y ber and in angular location -relative to the tank.

Between each aperture 25 and corresponding half-pipe I3, a semi-cylindrical distributing steel l duct 26 extends radially below and adjacent to the bottom I2, being welded to the cylindrical wall I9 at the inner end, to the free end IB-E of the fitting I6 at the outer end, and to the bottom I2 between these ends. 'I'hese ducts 26. again, are half-pipes, and are made like the vertical ducts I3. Thus the central distributing sump communicates with the six vertical halfpipes by six more or less horizontal distributing members; and these, at the same time, serve to reinforce the tank bottom.

The tank I@ is subdivided into an inner clarification and sludge filtration zone 2l of great area and an outer, or peripheral iiocculation Zone or channel 23 of smaller area, by a cylindrical steel baille or wall 23 installed concentrically with the tank and extending from the open top of the tank to above the bottom I2. Each of these two zones preferably lls at least the major part of the depth of the tank; however, only the clariication zone and not the occulation zone, as shown, extends up to the very top, and the uppermost part of the outer channel functions as a .scum release zone 3G, by virtue of radial stilling baiiles made of steel plates Si, spanning at least part of the depth of this top part, at close angular distances from one another. g These 'stilling bafe plates can serve or cooperate at the same time to center and to support the cylindrical baiiie 29.,

The cylindrical baiiie, in turn, may carry now deecting baiiles 32 radially projecting into a lower part of the clarification zone 2l, above the bottom l2; the inner ends of such deflecting baffles being spaced from one another and held rigid by a cylindrical holding ring 33 welded thereto. The diameter of the holding ring 33 generally is about one-quarter to two-fifths that of the large baille 23.

The inside `of the large, cylindrical baffle 29 carries also an annular effluent launder 34, adjacent the top of the tank. 'This launder is supported by radial brackets or gusset plates 35, preferably welded to the large, cylindrical baille 29 alonglines opposite the weld seams connecting the outer, supporting plates 3| to the large, cylindrical baiiie 29. The launder comprises upstanding walls 36, having top edges 3l which serve as overflows, determining the lowest level 38, to which the water in the clarincation zone can fall after the tank has been iilled; the uppermost water level being controlled in usual manner, by means not shown. y

The top of the tank wall I I is reinforced by an annular, flanged beam 33, and supports two straight, parallel, transverse beams d@ which span the tank. Between these transverse beams, in the center of the tank, we install a drive assembly 4I, which need not be described in detail. These transverse beams may serve or cooperate,

The drive 4I and propeller 41 are adapted to" induce a downward fluid ow through the zone occupiedy by the propeller. A central` transfer passage 53 is provided, between the open bottom rend of the drum 45 and top of the guide 23, outside'of this guide; and outer transfer passages 54 are provided between the top parts of the vertical half-pipes' I3 and the channel 28, through the tank wall I I. Thus the propeller 4l is adapted to induce fluid circulations through a system of closed pathways passing fromthe zone of propeller 4'I through the Water mixing zone 52, distributing sump I8, distributing half-pipes 26, vertical half-pipes I3, outer transfer passages 54, occulating channel 28, the bottom part 2l-A of the sludge filtration zone 21, central transfer passage 53, and lchemical mixing zone 5I, back to the zone of propeller'4l. l

The aforementioned zones 53, 5I, 52, I8, 26, I3, and 54 are generally dimensioned so that,von

. proper rotation of the propeller 41, a mixture of in some instances, to hold the large, cylindrical baille 29 and parts mounted thereon, We provide access to the drive assembly by a Walkway d2, installed between the beams and protected by handrails 43, as usual,

Depending from the drive assembly di, we provide an agitator and circulator Ishaft @it adapted to rotate rapidly,l and a drum 55, concentrically surrounding this shaft and adapted to rotate slowly. e

The rapid shaft 44 extends downwardly into the interior of the liquid guide member 23 to a point adjacent the discharge end of vthe nipple 22, where it is centered by a bearing 45; a pumping and circulating propeller 47 being carried by the shaft immediately above the bearing 46. A flexible Icoupling 48 is interposed on the shaft. The shaft also carries straight, radial stirring paddles 49, in the zone above the propeller 4l and within the drum .45 and guide member 23.

This zone receives the newly incoming chemical reagents, if any, through apipe 50 entering at the top, and is identified as chemical mixing water and sludge which has been properly pretreated in a manner to be described, passes continuously through all of said zones at a velocity within the approximate range of one to two feet per second (720 to 1440 inches per minute) although in some instances, and at some points, limiting liquid velocities as low as about 6 inches per second or -as high as about 5 feet per second (360 to 3600 inches per minute) may be reached. This general range of velocities of about 1000 inches per minute, more or less, is identified as mixing and transfer velocity, 'I'he complete passage53, 5I, 52, I8, 26, I3 and 54, wherein such a mixing and transfer velocity prevails, is identified asa mixing and transfer zone, with the to sixty, or generally about thirty seconds, more or less, not counting the central passage 53 and the chemical mixing zone 5I.

In front of the transfer passages 54, in the occulating zone 28, guide baiiles 55 are installed to deflect all of the incoming circulating uid from the several distributing half-pipes i3 into a single, approximately circular or helical pathway `coinciding with the annular locculating zone 23, as indicated by the arrows 5B in Fig. 2. For this purpose, we provide rectangular baille plates welded to the inside/of the wall II adjacent to the outer transfer passages 54, as shown at 5l, at an acute angle with the wall, s o as to avoid any substantial restriction of the annular pathway 56 and to make sure that the local eddies 58, which are unavoidably formed past the baffles 55, are not so large as to unduly interfere with the desired, circular movement of the'liquid in the annular channel zone 28. Preferably, we make the passages 54 rectangular, somewhat smaller in area than the half-pipes I3, and with the long side vertically disposed. We shape and place each deiiector baille 55 so that the passage 59 between the baille and the wall Il forms a nozzle having a gradually expanding area, to insure gradual recovery of head, and absence of `excessive eddies 58. No horizontal guides for the around, vertically disposed along, and integrally' welded to the inside of the annular wall or baille 29. These half-pipes I3-A yand the baille 29 welded thereto may be supported, as well as supplied with circulating liquid, from the bottom of the tank adjacent the inside of the occulation channel. 28, as shown. As a result, it is of course impossible to scrape sediment from the bottom of the flocculation channel 28 by scrapers pivoted in the center of the tank. For this reason, a concrete corneriill I2-A may be provided in the bottom of said channel, having sufficient inward slope to cause any sludge settling thereon to slide inwardly and downwardly into the bottom part oi the clariiication zone, where -the Scrapers operate.

The dimensions of the peripheral iiocculating 2,2, or leaving through the launder 3l', by the area of the sludge bed zone 21, more particularly by the area of theupper clarification zone 21-B, forming the upper part of this zone 21 and which is substantially unobstructed by sludge. The rising rate must not besubstantially higher than indicated, because otherwise, the top of the sludge bed, filter or blanket 60 would rise to a level dangerously close to the weirs 31, and in the body of the sludge bed, insuiiicient contact of water and sludge would be maintaine The clarifical Vtion and sludge filtration zone is so dimensioned,

with respect tothe maximum or capacity amounts of raw liquid entering through the nipple 22, as to provide a detention time of about 40 to 120 minutes, with an average of about 60 minutes. l

The throughput velocity, if any, is augmented bythe circulationinduced by the propeller lil;

channel 2d are such that the liquidxvelocity, in the circular or helical pathway 56, is further diminished to a considerable extent, after the gradual decrease, in the passages 59, from the mixing and transfer velocity. Generally, we provide for a horizontal liquid circulation at a speed of alo-out one to fifteen inches per second (60 to 900 inches per minute), with a preferred, average velocity of about 5 inchesper second (300 inches per minute), in the horizontal plane adjacent the centers oi the outer Vtransfer passages tl. This range of liquid velocities, about 300 inches per minute, more or less, is identied as ilocculating velocity, and is generally conducive to the formation oilarge and heavy ilocs, in a liquid treatment as contemplated herein. Such ilocculating velocity mayalso be conducive to the settling of at least some ocs, of greatest settleability, while the bulls cf the ocs are generally entrained by the liquid horizontally circulating at such a rate. Of course, in a plane adjacent the bottom l2, in the flocculating zone v28', and parts'of the clarification zone 2l, somewhat -slower velocities prevail, which however, are still in the range of i'locculating velocities; a smooth, annular, substantially unobstructed passageway 56 being provided throughout at least a major portion of the fiocculating zone 28. The flocculating zone is so dimensioned as to .provide a detention period of about two to six minutes for the ow of liquid mixed with recirculated sludgegenerally about ve minutes.

The clarification and sludge filtration zone 21, as mentioned, has greater area than the ilocculation channel 28. Any throughput flowthrough this clarilcation zene is generally upward, towards the weirs 31, andrmust be kept within a range of maximum r-ates of not more than about 2 or 4 inches per minute, depending on the specic type of treatment. Thisrange of about 3 inches per minute, more or less, is identified as capacity rising rate. It is calculated by dividing the amount of water entering through the nipple and this results in the aforementioned increased total velocities Vin certain parts of the clarification zone, as well as elsewhere. I l

This circulation passes through the bottom part 2-1 A of the clarication zone, over the bottom l2, in spiral directions, due to the previous Icir cular or helical ow. The velocity of this spiral 'iiow over thev bottom I2 is approximately that prevailing inthe' bottom part of the flocculation' channel; it is somewhat less in the outer parts of the zone 21-A, due to the slight loss of head and velocity incident to turning around the lower end of the annular baille 29; and the linear ,ve. locity may be greateradjacent the center of the zone 21-A, where the propeller t1, through the central transfer passage 53, exerts a suction eect on this spiral flow, and where a vortex may be formed. The spiral flow in the zone 2li-A serves the purpose of distributing the liquid to be treated throughout the bottom part of the sludge filter iid, and the said velocities Aof this spiral flow are identied as distributingv'velocities.

Parts of the spiral flows in the zone 2li- A are vertically 'deflected by the radial baffles 32, resulting in upward ows in front of each baffle 322.

If these baliies are closely spaced, such upward flows may be negligible, and the baflles are then referred to as stilling baiiles. With increased distances between the bailies 32, a more substantial upward iiow will Aoccur in front of each baffle and the baiiies are thenidentiiied as deilectors. These upward iiows serve the function of suspending 'some of the sludge up to highe'i levels than would be reached otherwise in the sludge bed tt; their velocities are identified as sludge suspending velocities, and are generally maintained within a range of about 5 to 60 inches per minute, by a proper arrangement of the baiiles 32. The actual velocity of each upward, sludge suspending iiow tends to decrease rapidly as the flow proceeds upwardly, due to the dropping off of large and heavy sludge particles, and downward entrainment of liquid particles by the same. Thusan upward, sludge suspending ilow, at a ydecreasing rate, in front of each baille 32, is accompanied by a slower, downward I'lowcompleting what is identified as a secondary, vertical circulation. Such secondary circulations take place between the baiiles 32 and sometimes up to a level above these baffles. However, secondary circulations at appreciable velocities are prevented from reaching thetop of the tank, by said arrangement of the baffles, and other factors. The precise directions and average velocities of these vertical circulations depend on the composition and temand the distances between the baiiles 32. The average velocity of the secondary circulations, called secondary circulating velocity, generally amounts to about 10 inches per minute, more or less, depending on the various factors mentioned, which must be selected and empirically controlled to suit the Aparticular conditions ofeach treatment and locality. Higher secondary velocities can be used sometimes, especially where excess sludge is removed at an elevated point, and where the sludge has a high specific gravity.

The various average, approximate velocities and detention periods mentioned can be resumed and tabulated as follows:

Zone vVelocity Detention Period fia/min. min. Mixing and transfer... 1000 (throughput .5 (throughput and and circulation). circulation). Flocculating 300 (through ut and 5.0 (throughput rculation and circulation). Distributing 300 igtlixiogh ut and c a on 00.0 (throughput Sec. Circulatin l (throu hput and g crculat on). a1ne)` Upper Clarication 3 (throughput alone) In operation, circulation is constantly induced and maintained by the propeller "fand any throughput flow received is combined therewith in the water mixing zone 52. Inmany instances, the -circulation is uniform and relatively rapid, and involves greater amounts of flow than are brought in even by the maximum or capacity input, in order to safely suspend a sludge bed regardless of variable throughput flows. The combined iiows proceed through the transfer zone, at the rapid transfer velocity. This results in intimate admixture of the new water, recircu-r -On the other hand, the largest particles are ultimately eliminated by gradual sedimentation, and this occurs mainly in the sludge bed 30, although sedimentation may start in the occulation zone 20.

The aforementioned secondary circulating and capacity rising velocities are very critical, since for best results, they should (l) induce a m imum of sludge build-up in the sludge bedrut also (2) allow proper sedimentation in this bed, and nally, ofcourse, (3) prevent objectionable boilupsl of dense clouds of sludge towards the overflow Weirs. The velocities must and can be empirically balanced, by adjustment of the circulator drive, when a tank of this type is put in operation; and re-adjustments may be required from time to time, especially if the character of the raw water is subject to change.

Of coursethis equilibrium of conditions and tendencies in the sludge bed must not be disturbed by excessive surges. 'However, surges do occur sometimes, in any water supply system. Any surges, inherently, tend to spread through the inlet nipple and transfer passages into the occulation zone and from there, at a decreased but Furthermore, the design involving the Ncylindrical baille 33 is an aid towards avoiding bad effects of relatively major surges. When such surges arrive in the sludge bed, they are generally local in character, not uniformly distributed.

'I'hey are felt most strongly in the central part,

where the spiral distributing'ilow has a maximum velocity. The central cylindrical zone 6|, defined by the cylindrical baille 33, is unobstructed, and allows horizontal equalization of substantial surges, thereby preventing objectionable boilups.

In order to put our tank in operation, and to re-start it after a shutdown, we have to provide a sludge bed, in well-known manner. Such starting and re-starting operations are facilitated by the construction of the inlet to the central transfer passage 53, as shown in Figs. 3 and 4.

The drum 45 is open at the bottom, and provides a bottom inlet 62, between the inside of the drum and the outside of liquid guide member- 23. As shown in Fig. 3, the outside of the conical portion of this liquid guide member is relatively close to the inside of the drum, adjacent this bottom inlet 62, so that the area of this bottom inlet is relatively small, and when all of the circulating liquid enters here, the quantity is limited but the velocity thereof is within a relatively high section of the range of transfer velocities.

The drum 45 also has side inlets 63 to the passage'53, and gates 64 to control these side inlets. These gates are guided by vertical tracks 65 se'- cured` to the drum 45. Each gate has a projecting lug 66, with a vertical hole 61 through the same, and a vertical rod 68 extending through and upwardly from this hole and secured to the -lug by bolts 69; the bottom of the rod being threaded. 'Ihe rods 68 are used to raise and lower the gates 64, in obvious manner, which need not be described as to mechanical details.

Preferably, all gates are lowered before and during a starting or restarting operation. As a result, sludge can be picked up, recirculated and re-supplied to the ilocculating and sludge filtration zones, soon after the beginning of a starting or re-starting operation, through the restricted opening 02 at the lowest point of the drum d5. All gates are preferably raised for normal opera-l tion, so that large amounts of suspended sludge can be recirculated through the enlarged passages 62 and 63, with a minimum of restriction, sludge break-up, and wastage of power.

These gates 64 can be used also to adjust the rate of sludge recirculation, which, as mentioned, is of great importance for a proper equilibrium of conditions in the sludge bed. With proper 'dimensions of the drum 45, guide 23, and side openings 63, the circulating velocity can be controlled over a wide range, with or without a variable drive in the unit 4|.

The sludge settling on the bottom l 2 is collected by Scrapers 10 on trusses Il secured to the slowly rotating drum 45. The collected sludge accumulates adjacent the center of the tank, in a conventional sludge sump 'l2 depending from the bottom l2, until it is ultimately withdrawn in well-known manner.

Certain parts of this device can be pre-fabricated with advantage. This applies mainly to the sub-assembly of the drumY 45 with the gates 64; the sub-assembly of the liquid guide 23, vanes water.

posts", and submerged in the grant-8i.

nipples 9| extend to the outside of said grout, and 75 599,176

9 24 and nipple 22; the sub-assembly of the cylinder I9 and plate 20; the fittings IB; and, of course, the drive unit, the agitator, thescraper trusses, and the sludge sump.A

various modifications can be applied.

For instance, Fig. shows the tank supported by modiied half-pipes 13, which at the bottom ends terminate in full pipe sections 14 having ilanges 15 secured thereto. Such combined halfpipes and full pipes 13, 14 can be formed, for instance, by taking ordinary pipes and cutting oi semi-cylindrical portions thereof over a' portion of their length.

` The flanges 15 distribute the weight supported by the half-pipes over Wide concrete surfaces in the support posts 16, by meansv of vertical bolts 11 secured to the flanges 15 by nuts 18 and also having washes 19 secured thereto by bolts 80', submerged in the concrete.. The nuts 18 on the bolts 11 and anges 15 also serve to level the tank. Before the tank is loaded with water, the weight can be supported by the bolts, and the ilanges 15 are spaced above the concrete posts 16. The units can then be turned up or down until th'e tank is properly positioned to insure horizontal rotation'of the scrapers 10 and horizontal position of the weirs 31. Thereafter, `th'e spaces between the iianges 15 and concrete posts 16 are shrouded by suitable forms as shown in dotted lines, and a uid grout 8| is then forced into said spaces through openings- 82 in the flanges 15. When this grout has solidied, the forms can beremoved, and the tank loaded with 'Ih'e full pipe section 1l can be so dimensioned and arranged as to properly support the weight oi the tank when loaded. The half-pipes 13, alone, of course have ionl'y one-half of rthe strength of such full pipe sections, but are reinforced by being welded to the tank wall I l. The conduit sections 83 between the half-pipes 18 and null pipes, adjacent the lower end of the tank provide clean-out openings for the distributing and supporting conduits.

`Additional, larger openings, surrounded by flanges 93, may be provided in the vertical conduits opposite the distributing pipes 85, and closed by plates 94, held by bolts 95 and nuts 96, with gaskets 91 interposedbetween these flanges and plates, to provide access for inspection of the conduits, after the tank has been substantially drainedth'rough the smaller cleanouts 92.

Still other modifications may occur to persons skilled in this art. 1

We claim:

l. A liquid treatment tank comprising a bottom; a substantially cylindrical sidewall; an annular baille in the tank, secured to said wall, extending downwardly to above said bottom and separating an outer flocculation chamber from an inner7 clariiication and sludge filtration chamber in said tank; a series of hollow pilasters distributed around said wall on the outside thereof,

wall Il, are relatively 'poorly reinforced by the tank wall, and are therefore, desirably provided with' reinforcing ribs 84 welded to the outside of 'such conduit sections opposite the wall l I.

In the embodimentof Fig. 5, the distributing conduits 85 are shown as full pipes horizontally installed between the centraldistributing sump andthe vertical conduits, and communicating with the full pipe sections 14 of the latter, immediately above the nanges 15.l The bottom l2 is reinforced by beams 88 welded thereto rather 'than This modification by the distributing conduits. is advantageous if and when distributing conduitsof proper size to carry th'e flow at said mixing and transfer velocities are too feeble to reinforce the bottom sufliciently. `The beams 88 are loaded largely with transverse bending stresses. whereas the vertical halt-pipes are loaded mainly with longitudinal compression stresses, which are more readily absorbed by halt-pipes.

The vertical full pipe sections 14 are preferably closed by plates 87 secured to the flanges 15 by the bolts 11 and nuts 18, with gaskets 88 interposed between the flanges and plates, and the plates having the same outer diameter as the danses. central weld iittings 89 v having street ells 90 threaded `into lthe same, and nipplesl threaded intoysaid street'ells'and closed by caps 92. These lweld ttings and street ells maybe disposed in Ih'e plates 81 are shown equipped with the spaces between the flanges 15 and concrete The..

ing to a lower inside part of one of said hollow.

pilasters, and each of said hollow pilasters having an upper inside part communicating through said wall with' an upper part of said outer chamber; means to circulate liquid from said central part of the tank outwards through said conduits, upwards through said hollow pilasters, downwards through said outer chamber, and inwards over said bottoms in saidfinne'r chamber to suspend sludge therein for sludge filtration; means to introduce any required chemical reagents and the liquid to bevtreated thereby into said circulated liquidto form said sludge, and means to withdraw reated liquid from the top of said inner cham- 2. An elevated liquid treatment tank according to 'claim 1, combined with a series of columns; each of said hollow pilasters being supported by one of said columns, and at least a substantial portion of the'weight of said tank and its contents being supported by said columns and hollow pilasters.

3. A liquid treatment tank according to claim l, wherein each of said conduits leading from the central part of the tank to the respective pilaster comprises a hollow member extending along and secured to the .under side of said bottom.

.LAWRENCE W. BEKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,900,809 Hammerly Mar. 7, 1933 -2,076,529 Durdin Apr. 13, 1937 2,245,588 Hughes June 1'7, 1941 2,245,589 Hughes June 17, 1941 2,348,123 Green et al May 2, 1944 2,355,069 Green Aug. 8, 1944 2,263,167 Dorr et al. Nov. 18, 1941 806,214 Trent Dec. 5, 1905 2,073,784 Day Mar. 16,' 1937 FOREIGN PATENTS Number Country v Date 'French June 9, 1923 

